One-electron redox processes in a cyclic selenide and a selenoxide: A pulse radiolysis study

One-electron redox reactions of cyclic selenium compounds, DL-trans-3,4-dihydroxy-1-selenolane (DHS), and DL-trans-3,4-dihydroxy-1-selenolane oxide (DHS) were carried out in aqueous solutions using nanosecond pulse radiolysis, and the resultant transients were detected by absorption spectroscopy. Both OH radical and specific one-electron oxidant, Br radical reacted with DHS to form similar transients absorbing at 480 nm, which has been identified as a dimer radical cation (DHS ). Secondary electron transfer reactions of the (DHS) were studied with 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) and superoxide (O) radicals. The bimolecular rate constants for the electron transfer reaction between (DHS) with ABTS was determined as 2.4 ± 0.4× 10 M s . From this reaction, the yield of (DHS) formed on reaction with OH radical was estimated in the presence of varying phosphate concentrations. (DHS) reacted with O radical with a bimolecular rate constant of 2.7 ± 0.1× 10 M s at pH 7. From the same reaction, the positive charge on (DHS) was confirmed by the kinetic salt effect. HPLC analysis of the products formed in the reaction of (DHS) with O radicals showed formation of the selenoxide, DHS. In order to know if a similar mechanism operated during the reduction of DHS, its reactions with e were studied at pH 7. The rate constant for this reaction was determined as 5.6 ± 0.9× 10 M s, and no transient absorption could be observed in the wavelength region from 280 to 700 nm. It is proposed that the radical anion (DHS ) formed by a one-electron reduction would get protonated to form a hydroxyl radical adduct, which in presence of proton donors, would undergo dehydration to form DHS. Evidence for this mechanism was obtained by converting DHS to (DHS ) with the addition of DHS to the same system. Quantum chemical calculations provided supporting evidence for some of the redox reactions. © 2010 American Chemical Society.